Jamaican vomiting sickness, a long-known and extensively investigated illness caused by ingestion of unripe ackee fruit, is associated with severe metabolic derangements, resulting in hypoglycemia, various forms of encephalopathy, and in some cases, death. Chemical and biochemical studies have shown that methylenecyclopropaneacetyl-CoA, a metabolite of the nonprotein amino acid hypoglycin found in ackee fruit, brings about the illness through suicide inactivation of acyl-CoA dehydrogenase. No detailed understanding of this inactivation is available. We propose a variety of experimental studies to identify the products of the inactivation reaction and to learn how the reaction takes place. Preliminary work with synthetic methylenecyclopropaneacetyl-CoA and general acyl-CoA dehydrogenase will be extended with a series of isotopically labeled reactants. The results of these studies will establish the chemical and stereochemical course of the inactivation process and exemplify several novel approaches to suicide substrate inactivation chemistry, including the determination of deuterium isotope effects on inactivation kinetics, tritium-labeled inactivator/carbon-14 labeled enzyme product studies, and serial carbon-13 labeling of specific inactivator to secure and soundly interpret 13C NMR data for the inactivation product.